1. Field of the Invention
The present invention relates to a substrate transfer system for a liquid crystal display (LCD) device, and more particularly, to a system having an auto guided vehicle provided with a bar code reader and for transferring a cassette in which a substrate is loaded.
2. Description of the Related Art
Generally, an LCD device comprises a TFT array substrate and a color filter substrate bonded together by a sealant with liquid crystal filled therebetween. A liquid crystal display panel is usually formed of a glass substrate. Nowadays, a liquid crystal display panel of large size can be produced. However, it is difficult to transfer the liquid crystal display panel of large size, and therefore, there has arisen a need for a substrate transfer system to transfer a large sized substrate.
In the related art, a substrate is transferred by a cassette in which one or more substrates are loaded. The cassette is transferred to a stage of a corresponding step by an auto guided vehicle. The transfer system comprises a cassette stocker where a substrate cassette is stored; a robot arm for taking out the substrate cassette from the cassette stocker; an auto guided vehicle for transferring the substrate cassette; a rail on which the auto guided vehicle moves; a plurality of stages; and a main computer such as a host for controlling the auto guided system.
The substrate cassette transfer system in accordance with the related art will be explained with reference to FIG. 1.
First of all, substrates go through various processes, and substrates that have undergone the same processes are loaded in the same cassette and stored in the cassette stocker. That is, for example, substrates which have undergone a process for forming a gate line among processes for fabricating a thin film transistor as a switching device are loaded in the same cassette to be held or stored until next processes.
To perform predetermined processes using the substrates loaded in the cassette stoker, the substrate cassette is loaded on the auto guided vehicle from the cassette stoker. The process is performed by giving an order to the cassette stocker by the host. Therefore, the cassette stocker is provided with a receiver for receiving data from the host. The substrate cassette loaded on the auto guided vehicle is transferred to a process stage where a corresponding process will be performed. The auto guided vehicle moves along a predetermined path and, thus, arrives at a corresponding stage. The corresponding stage may be a fabricating apparatus for an LCD device including a chamber where various processes, for example, the cassette cleaning, sputtering, photo resist formation, etc. are performed.
Each stage includes a shelf for holding the transferred substrate cassette until use. The auto guided vehicle arrives at the corresponding stage and unloads the cassette where the substrate is loaded on the shelf of the corresponding stage using the robot arm of the auto guided vehicle. Also, a bar code reader formed at an arbitrary point of the shelf which is at one side of the stage reads a bar code attached to one side of the cassette to recognize the cassette, and then transmits data to the host. Accordingly, the host determines processes of a corresponding cassette.
If the bar code reader transmits the read information to the host, the host determines which process will be performed for the corresponding cassette and orders the process to progress or stop at the corresponding stage. The substrate which has undergone a specific process on the corresponding stage is reloaded into the substrate cassette. Then, the host calls an empty auto guided vehicle to load the cassette where the processed substrate is loaded and to transfer to the cassette stocker for storage.
However, in the substrate transfer system, the bar code reader has to be respectively provided on each stage, thereby increasing cost. That is, the bar code reader is an expensive device causing increased cost.